A team of amateur spelunkers has discovered caves filled with very well preserved fossils of giant flat-faced kangaroos, marsupial lions, wombats, Tasmanian tigers, and other megafauna that lived in Australia during the Pleistocene era, between 1.75 million and 10,000 years ago.

Paleontologists who have been investigating the cave, which is in a remote region of Australia's Nullarbor Plains in the state of Western Australia, have called it "the find of the century."

"A find like this comes along once in a lifetime, if you are lucky," said Gavin Prideaux, curator of the Naracoorte Caves collection at Flinders University in Adelaide and an expert on the Pleistocene cave fossils. "It was actually a pretty strange situation because with the first one, two, three specimens you feel you are over the moon with excitement, but everywhere we turned we found more stuff."

One of the most exciting discoveries is the first complete skeleton of a flesh-eating marsupial "lion," Thylacoleo carnifex, said John Long, curator of vertebrate paleontology at the Western Australian Museum in Perth, who led the three-week expedition, dubbed Operation Leo, at the site. To date eight skeletons of Thylacoleo have been found in these caves.

Thylacoleo is not a lion; it is more closely related to koalas and kangaroos. It is the largest carnivorous mammal ever to have lived in Australia and the largest known marsupial carnivore in the world.

At about two meters long, it was about the same size as a leopard, with massive paws and forearms, huge retractable claws, and enormous "opposable thumb-like" appendages that were probably used for tree climbing. Unlike the large cats that have two enlarged canines, marsupial lions had enlarged incisors that were used to stab prey.

Also among the caves' bounty are skeletons of up to 10 different species of extinct kangaroos; about 75 percent of the skeletons are complete, including three from giant kangaroos that were as tall as three meters (10 feet). There are also remains from the flat-faced giant kangaroo Procoptodon goliah, the largest of all kangaroo species.

Another juicy find is the fossil of a giant wombat the size of a small car.

Although many of the plants and animals that thrived during the Pleistocene are similar to their modern descendents, the period is known for its abundance of giant creatures: woolly mammoth, mastodon, saber-toothed cat, longhorned bison, wooly rhino, and giant ground sloth.

The structure of the Australian cave suggests it worked as a pit trap. The hole leading to the cave was covered with vegetation, said Long, and animals fell in and got trapped.

Entering the cave today requires wriggling through a 10-meter-long (32-foot-long) tunnel that runs from the ground surface to the roof of the cave. Then there is a 15-meter (50-foot) drop to the cave floor.

Death by Starvation

Even with the precipitous drop, Prideaux believes most of the giant animals that fell into the cave didn't die on impact. "It looks like they didn't die for a few days because each specimen was found curled up in a different nook," he said. "They probably walked around and eventually died of starvation and dehydration."

If the animals had died on impact, all the bones would have been found in a heap directly below the hole in the ceiling.

The paleontologists said the site is unique in part because of the distribution of the skeletons in three caves.

Fossil deposits from the Pleistocene era are usually a jumble of sediment-embedded bones from different skeletons, Long explained. Such piles are created as rain or floodwaters gush through the caves, washing the dirt and bones into a corner. Sorting though piles of bones to distinguish various extinct species, some of them perhaps unknown, can be extremely difficult, he said.

"Here the bones are completely undisturbed," said Long. "It is as if the animals just curled up in a corner and never woke up." The cave was probably sealed with dirt because there are no human remains or bones from any modern species.

The bones are in such good condition that Long collected DNA samples from several specimens, which he hopes to use to accurately date the remains. The DNA will also be used to establish evolutionary links to modern marsupials in Australia today.

The Nullarbor Plainsa vast, arid plateau stretching from South to Western Australia and bigger than the state of Texasare riddled with thousands of caves, but very few contain fossils. Even fewer have the dark, dry conditions necessary for preserving remains.

"Thus we have a very poor paleontological record of the flora and fauna from this area, until now," said Long. "This cave is one of the most important megafauna sites in the whole of Australia and offers a snapshot of the diverse collection of animals that existed during the Pleistocene period."

The cave was discovered by Father Ken Boland of St. Francis' Church in Melbourne, an avid caver and pilot who was conducting a survey of landscape features from his ultralight aircraft. Noting details such as soil color changes, holes, depressions, and fissures, he noticed an interesting feature and sent a ground team to explore.

The ground teammembers of the Australian Speleologial Federationentered the cave for an initial investigation, then withdrew without removing any of the fossil remains. The exact location of the cave is being kept a secret to protect it from looting by fossil hunters seeking specimens to sell on the black market.

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